Elevated serum cholesterol levels (&gt;200 mg/dL) have been indicated as a major risk factor for heart disease, the leading cause of death among Americans. As a result, experts have recommended that those individuals at high risk decrease serum cholesterol levels through dietary changes, a program of physical exercise, and lifestyle changes. It is recommended that the intake of saturated fat and dietary cholesterol be strictly limited and that soluble fiber consumption be increased. Strictly limiting the intake of saturated fat and cholesterol does not, itself, present a risk to proper health and nutrition. Even where saturated fat and cholesterol are severely restricted from the diet, the liver remains able to synthesize sufficient quantities of cholesterol to perform necessary bodily functions.
More recently, experts have begun to examine the individual components of the lipid profile, in addition to the total cholesterol level (TC). While an elevated TC is a risk factor, the levels of the various forms of cholesterol which make up TC may also be risk factors. Elevated low-density lipoprotein (LDL) is a cause for concern, as these loosely packed lipoproteins are more likely to lodge within the cardiovascular system leading to the formation of plaque. Low levels of high-density lipoproteins (HDL) are an additional risk factor, as they serve to sweep artery clogging cholesterol from the blood stream. A better indication of risk appears to be the ratio of TC:HDL.
A number of nutritional factors have been shown to improve serum cholesterol levels. For example, the use of phytosterols has been well documented in human clinical trials and in animal studies to lower serum cholesterol levels. This cholesterol lowering effect has been attributed to interference with the absorption of dietary cholesterol. Phytosterols, being structurally similar to cholesterol, competitively bind with cholesterol sterol receptor sites, thus preventing cholesterol uptake. Unlike their cholesterol counterparts, phytosterols are very poorly absorbed, and some are not absorbed at all. Therefore, phytosterols do not contribute to an increase in serum cholesterol levels. In addition to competing for receptor sites, phytosterols also compete for the enzyme cholesterol esterase. This enzyme is required by cholesterol for its breakdown to components which may be absorbed through the microvilli which line the wall of the small intestine. Thus, phytosterols also impede the enzymatic breakdown and intestinal absorption of cholesterol, which further reduces serum cholesterol levels.
Plant derived long-chained aliphatic alcohols have also been documented to reduce serum cholesterol levels in experimental models, healthy humans and in type II hypercholesterolemic patients. These aliphatic alcohols, collectively known as policosanol, have been employed in the treatment of elevated serum cholesterol levels in only the past five years, but policosanol has shown much promise, as reported in a number of published human clinical trials. The mechanism of action has not yet been elucidated, but policosanol's effectiveness is attributed to its influence on the bio-synthesis of cholesterol within the liver. This accounts for the ability of policosanol not only to decrease total cholesterol, but also to decrease LDL serum levels and increase HDL levels.